Process for the preparation of amine oxides

ABSTRACT

The present invention provides a process for the preparation of high quality amine oxide by reacting a tertiary or secondary amine with hydrogen peroxide as an oxidant in presence of a recyclable heterogeneous layered double hydroxide exchanged with one of the anions of transition metal oxides as a catalyst in a solvent selected from the group consisting of water, water containing dodecylbenzenesulfonic acid sodium salt as additive, and a water miscible organic solvent.

FIELD OF THE INVENTION

[0001] The present invention relates to an improved process for thepreparation of high quality amine oxides from secondary and tertiaryaliphatic amines. More particularly, the present invention relates to animproved process for the preparation of amine oxides from secondary andtertiary aliphatic amines useful in the preparation of hair conditionersand shampoos, toothpaste, laundry detergent powder, fabric softeners,toilet soap bars and cosmetics, surfactants as well as in otherapplications as synthetic intermediates and excellent spin trappingreagents.

BACKGROUND OF THE INVENTION

[0002] The N-oxides holds a key position in the chemistry ofheterocycles as well as in biomedical area. The tertiary amine oxidesare widely used in treatment of fabrics and preparation of hairconditioners and shampoos, toothpaste, laundry detergent powder, fabricsofteners, toilet soap bars and cosmetics as well as in otherapplications. They were also used as stoichiometric oxidants in metalcatalysed hydroxylation and epoxidation reactions of olefins. On theother hand, the oxides derived from secondary amines, called nitronesare highly valuable synthetic intermediates and excellent spin trappingreagents. In particular nitrones are excellent 1,3 dipoles and have beenutilized for the synthesis of various nitrogen containing biologicallyactive compounds e.g. alkaloids and lactams.

[0003] Conventionally tertiary amine oxides are prepared by oxidation ofrespective tertiary amines with strong oxidising agent like aqueoushydrogen peroxide in a solvent such as water, lower alcohol, acetone oracetic acid. A dilute or preferably concentrated (30-90% by weight)hydrogen peroxide solution is added in stoichiometric or greater amountto an aqueous solution containing the tertiary amine to obtain amineoxide, (U.S. Pat. No. 3,215,741). The drawback is that the reactiontransforms into a gel resembling a thick paste long before completion ofthe reaction which retards further reaction. The yields are only 30-40%by weight of amine oxide. Later several methods such as incorporation ofcatalyst and/chelating agent have been developed to in order to increasethe quality and yields of the product.

[0004] In case of secondary amines, the classical methods involve thecondensation of N-monosubstituted hydroxylamines with carbonyl compoundsor the direct oxidation of N,N-disubstituted hydroxylamines. Laterdirect oxidation of secondary amines using several oxidising systemssuch as R₂C(μ-O₂), Na₂WO₄—H₂O₂, SeO₂, TPAP-NMO and UHP-M (M=Mo, W),MTO-H₂O₂ have been developed to accomplish nitrones under homogenousconditions. The drawback in all the above cases is the difficulty inrecovering the homogeneous catalyst/reagents from the reaction mixture.

[0005] Reference may be made to a U.S. Pat. No. 3,283,007 wherein theoxidation of tertiary amines using diethelene triamine penta/tetraacetic acid as chelating agent and sometimes contaminated with heavymetals is recommended to improve the yield. The hydrogen peroxidesolution employed has concentration of at least 30-75% by weight. Thedisadvantages of this process are high reaction temperatures rangingbetween 40-100° C., longer reaction periods, and lower yields of amineoxides.

[0006] Reference may be made to U.S. Pat. No. 3,424,780, wherein highyields of tertiary amine oxides are achieved by carrying the oxidationof tertiary amine with 30-70% by weight of aqueous hydrogen peroxideusing 0.01 to 2% weight of carbondioxide, in presence of a chelatingagent, tetra acetylene diamine, a salt thereof, polyphosphates,stannates, a hydroxy carboxylic acid salts or the salt of polycarboxylic acid. The reaction is carried out at a temperature rangingfrom 40 to 80° C. The disadvantages of this process are high reactiontemperature, longer reaction periods and the amine oxide formed isintensively coloured when carbon dioxide atmosphere is used to speed upthe reaction and this method necessitates injecting a gas which requireshandling facilities. Another disadvantage is more than 30% by weight ofhydrogen peroxide is not environmentally friendly.

[0007] Reference may be made to another U.S. Pat. No. 4,889,954 whereinthe tertiary amines are reacted in high yields to give the correspondingamine oxides with a low content of nitrosamine, the oxidation oftertiary amine being carried out in the presence of a dialkyl carboxylicacid ester as catalyst and if appropriate, ascorbic acid as aco-catalyst using 45-70% by weight of hydrogen peroxide. The drawbacksin the above process are the requirement of frequent addition of waterto avoid gel formation, high reaction temperatures, longer reactionperiods and difficulty in separation of the catalyst from the reactionmixture.

[0008] Reference may be made to another U.S. Pat. No. 4,565,891 whereinoctacyano molybdate or iron salts are used as catalysts and molecularoxygen for oxidation of tertiary amines at high pressures andtemperatures. The main drawback of this process is the need of very hightemperature of 90-130° C. and very low yields of amine oxide reporting11-52% of conversion.

[0009] Reference may be made to a U.S. Pat. No. 5,130,488 wherein thesolid amine oxide can be prepared by reacting a tertiary amine withhydrogen peroxide using carbon dioxide in presence of acetate andcooling to precipitate the product. This process is superior topreviously known methods of preparing amine oxides. However, its use cansometimes lead to cleavage of the solvents, plating on the walls of thevessel used for the precipitation, contamination of the product withresidual peroxide, and or discoloration of the product.

[0010] Reference may be made to a publication by Walter W. Zajac et al.,J. Org. Chem.; 53, 5856, 1988 wherein the oxidation of secondary andtertiary amines using 2-sulfonyloxyxaziridines (Davis Reagents) werereported. The drawback of the above process is, the reagent was used instoichiometric amounts.

[0011] Reference may be made to a publication by Shun-Ichi Murahashi etal, J. Org. Chem.; 55, 1736, 1990 wherein the sodium tungstate was usedas catalyst for the oxidation of secondary amines. The drawback is thedifficulty in recovery of the catalyst from homogeneous conditions.

[0012] Another reference may be made to publication by Murraay et al.,J. Org. Chem.; 61, 8099, 1996 wherein methyltrioxorhenium was used as acatalyst in oxidation of secondary amines. The drawback is thedifficulty in recovery of the catalyst.

OBJECTS OF THE INVENTION

[0013] The main object of the present invention is to provide aneco-friendly and simple process for N-oxidation of secondary andtertiary amines using layered double hydroxides exchanged with anions oftransition metal oxides as a catalyst, which is cheaper, non-corrosiveand recyclable catalyst utilising only lower percentage of hydrogenperoxide at room temperatures to give high yields of product.

[0014] Another object of the present invention is to provide an improvedprocess for the preparation of tertiary amine oxides and secondary amineoxides (nitrones), widely used in detergents, shampoos, fabric softersand biomedical area.

[0015] Another object of the present invention is the use ofnon-corrosive and low cost heterogeneous catalyst i.e. layered doublehydroxides exchanged with tungstate, molybdate, vanadate and theirpolyanions.

[0016] A further object of the invention is to provide a environmentallyfriendly process for the preparation of tertiary amine oxides andnitrones, using water alone or in combination withdodecylbenzenesulfonic acid sodium salt as an additive.

SUMMARY OF THE INVENTION

[0017] Accordingly, the present invention provides an improved processfor the preparation of amine oxides of a very high quality whichcomprises reacting tertiary and secondary amines with hydrogen peroxideas an oxidant in presence of a recyclable heterogeneous catalyst,layered double hydroxides exchanged with anion of transition metaloxides, with tungstate, molybdate, vanadate, and their polyanions i.e.polyoxometallates, in a solvent selected from water, water containingdodecylbenzzenesulfonic salt additive or a water miscible organicsolvent at a temperature ranges between 10-25° C. for a period of 1-6hours under continuous stirring and separating the product by simplefiltration and subsequently evaporation of solvents by known methods.

[0018] In an embodiment of the present invention, the heterogeneouscatalyst used is the layered double hydroxides exchanged with transitionmetal oxides selected from a group consisting of tungstate, molybdate,vanadate and their polyanions i.e. polyoxometalates. Having formula I:[M^(II) _((1-x))M^(III) _(x)(OH)₂][M^(II)]_(x/2).zH₂O, which is derivedfrom LDH having formula II [M^(II) _((1-x))M^(III)_(x)(OH)₂][A^(II−)]_(x/2).zH₂O where M is a transition metal oxidesselected from the group consisting of W, Mo, V and A^(n−) isinterstitial anion, selected from nitrate, chloride and M^(II) is adivalent cation selected from the group consisting of Mg²⁺, Mn²⁻, Fe²⁻,V²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ Pd²⁺, or Ca²⁺ and M^(III) is a trivalent ionselected from the group consisting of Al³⁺, Cr³⁺, V³⁺, Mn³⁺, Fe³⁻, Co³⁻,Ni³⁺, Rh³⁺, Ru³⁺, Ga³⁺ or La³⁺.

[0019] In another embodiment of the present invention, the tertiaryamines used are having the general formula R¹R²NR³ wherein R¹, R² andR³, which may be the same or different, and are the straight-chain orbranched-chain groups selected from alkyl, alkenyl and aralkyls havingC₁-C₂₄ carbons selected from N,N-dimethyl decyl amine, N,N-dimethyldodecyl amine, N,N-dimethylbenzylamine, triethylamine, tributylamine andcyclic amines selected from imidazolines pyrididines, N-substitutedpiperazines, N-substituted piperadines or N-substituted morpholines,e.g., N-methylmorpholine.

[0020] In another embodiment of the present invention, the secondaryamines used are having general formula R¹R²NH wherein R¹ and R² may bethe same or different and are the straight-chain or branched-chaingroups selected from alkyl, alkenyl and aralkyls having C₁-C₂₄ carbons,selected from dibutyl amine, dibenzyl amine, N-benzyl phenethylamine,N-phenyl benzylamine and cyclic amines selected from piperidine,1,2,3,4, tetrahydro isoquinoline.

[0021] In another embodiment of the present invention aqueous hydrogenperoxide is added slowly in a controlled manner for a period rangesbetween 0-120 min.

[0022] In yet another embodiment of the present invention, the catalystintroduced in the system is 6-12% by weight of anion of transition metaloxides selected from tungstate, molybdate, vanadate and their polyanionsas polyoxometalates.

[0023] In still another embodiment of the present invention, watermiscible organic solvents selected from group consisting of methonol,ethanol, isopropanol, 1-propanol, 1-butanol, 2-butanol and isobutylalcohol are used.

[0024] In still another embodiment of the present invention, the amountof hydrogen peroxide used is 2 to 6 moles per mole of amine.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The catalyst of the invention comprises a recyclableheterogeneous catalyst, i.e. layered double hydroxides exchanged withtungstate, molybdate, vanadate and their polyanions i.e.polyoxometalates that catalyses oxidation of secondary and tertiaryamines in a water miscible organic solvent, water or in water withdodecylbenzenesulfonic acid sodium salt as an additive. The advantagessuch as low cost of the catalyst, reusability for several times and itsability to oxidise the amines at 10-25° C., below or at room temperaturein a shorter period make the present invention as a promising candidatefor a clean and efficient industrial route to amine oxide preparation.

[0026] Parent/Copending application Ser. No. 09/721,585 discloses aprocess for the process for the preparation of amine oxides of highquality by reacting tertiary and secondary amines with hydrogen peroxideas an oxidant in presence of a recyclable heterogeneous catalyst,layered double hydroxides exchanged with anion of transition metaloxides, with tungstate, molybdate, vanadate, and their polyanions i.e.polyoxometallates, in a water miscible organic solvent at a temperatureranges between 10-25° C. for a period of 1-6 hours under continuousstirring and separating the product by simple filtration andsubsequently evaporation of solvents by known methods.

[0027] The novelty of the present invention lies in the use ofheterogeneous catalyst for the first time for the N-oxidation ofsecondary and tertiary amines. The anion of transition metal oxidesintercalated in the layered double hydroxide effectively catalyses theoxidation of amines to amine oxides. The catalyst was removed by simplefiltration and the solid catalyst obtained thus is recycled for severaltimes without any addition of fresh catalyst. The consistent activityfor several cycles, mild reaction conditions, shorter reaction timesmakes the process economical and possible for commercial realisation.

[0028] According to the invention, amine oxides of a very high qualityare prepared by reacting tertiary and secondary amines with hydrogenperoxide as an oxidant in presence of a recyclable heterogeneouscatalyst layered double hydroxides exchanged with anion of transitionmetal oxides, with tungstate, molybdate, vanadate, and their polyanionsi.e. polyoxometallates, in an organic solvent at a temperature rangesbetween 10-25° C. for a period of 1-6 hours under continuous stirringand separating the product by simple filtration and subsequentlyevaporation of solvents by known methods.

[0029] The heterogeneous catalyst used is the layered double hydroxidesexchanged with transition metal oxides selected from a group consistingof tungstate, molybdate, vanadate and their polyanions i.e.polyoxometalates. Having formula I: [M^(II) _((1-x))M^(III)_(x)(OH)₂][M^(n−)]_(x/2).zH₂O, which is derived from LDH having formulaII [M^(II) _((1-x))M^(III) _(x)(OH)2][A^(n−)]_(x/2).zH₂O where M is atransition metal oxides selected from the group consisting of W, Mo, Vand A^(n−) is interstitial anion, selected from nitrate, chloride andM^(II) is a divalent cation selected from the group consisting of Mg²⁺,Mn²⁻, Fe²⁻, V²⁺, Co²⁺, Ni²⁻, Cu²⁺, Zn²⁺ Pd²⁺, or Ca²⁺ and M^(III) is atrivalent ion selected from the group consisting of Al³⁻, Cr³⁻, V³⁺,Mn³⁺, Fe³⁺, Co³⁺, Ni³⁺, Rh³⁺, Ru³⁺, Ga³⁺ or La³⁺.

[0030] The tertiary amines used have the general formula R¹R²NR³ whereinR¹, R² and R³, which may be the same or different, and are thestraight-chain or branched-chain groups selected from alkyl, alkenyl andaralkyls having C₁-C₂₄ carbons selected from N,N-dimethyl decyl amine,N,N-dimethyl dodecyl amine, N,N-dimethylbenzylamine, triethylamine,tributylamine and cyclic amines selected from imidazolines pyrididines,N-substituted piperazines, N-substituted piperadines or N-substitutedmorpholines, e.g., N-methylmorpholine. The secondary amines used havegeneral formula R¹R²NH wherein R¹ and R² may be the same or differentand are the straight-chain or branched-chain groups selected from alkyl,alkenyl and aralkyls having C₁-C₂₄ carbons, selected from dibutyl amine,dibenzyl amine, N-benzyl phenethylamine, N-phenyl benzylamine and cyclicamines selected from piperidine, 1,2,3,4, tetrahydro isoquinoline.

[0031] Aqueous hydrogen peroxide is added slowly in a controlled mannerfor a period ranges between 0-120 min. The catalyst introduced in thesystem is 6-12% by weight of anion of transition metal oxides selectedfrom tungstate, molybdate, vanadate and their polyanions aspolyoxometalates. The water miscible organic solvents are selected fromgroup consisting of methonol, ethanol, isopropanol, 1-propanol,1-butanol, 2-butanol and isobutyl alcohol are used. The amount ofhydrogen peroxide used is 2 to 6 moles per mole of amine

[0032] Scientific Explanation

[0033] The catalytic cycle in the oxidation of amines to amine oxidesinvolves the easy formation of peroxotungstate, HOOWO₃ ⁻/HOOWO₆ ⁻ oninteraction of tungstate with hydrogen peroxide. These peroxy specieswill act as an active species for the oxidation of secondary/tertiaryamines as described by Murahashi et.al., for the Na₂WO₄ catalysedoxidation of secondary amines by hydrogen peroxide. The secondary amineundergoes nucleophilic reaction with peroxotungstate species to givehydroxylamine. Further oxidation of hydroxylamine followed bydehydration gives nitrone. In case of tertiary amines, the oxygentransfer occurs from peroxotungstate species to tertiary amine in asingle step to form tertiary amine oxide. The species HOWO₃ ⁻/HOWO₆ ⁻thus formed is readily oxidized with another molecule of H₂O₂ to giveperoxo tungstate HOOWO₃ ⁻/HOOWO₆ ⁻, thus completing the catalytic cycle.

[0034] The following examples are given by way of illustration of thepresent invention and therefore should not be construed to limit thescope of the present invention.

EXAMPLE 1 Preparation of the Various Catalysts 1. Preparation of Mg—Alhydrotalcite (LDH) chloride

[0035] Mg—Al—Cl hydrotalcite (3:1) is prepared as follows: About 200 mlof decarbonated and deionised water was taken into a 1 liter four neckedround bottomed flask and stirred at 25° C. with a magnetic stirrer undera nitrogen flow. The mixture (Al³⁺=0.05 mol/l), (Mg²⁺=0.15 mol/l) ofdecarbonated solution of AlCl₃.9H₂O (12.07 g), MgCl₂.6H₂O (30.49 g)(obtained from M/s. Fluka, a Sigma Aldrich Company, Switzerland) andaqueous solution of sodium hydroxide (16 g, 0.2 mol/l) were addedcontinuously drop-wise from a burette, the pH of the reaction mixturebeing kept at 10.00-10.2 during the reaction. The precipitate obtainedwas filtered, washed with deionised and decarbonated water and dried at70° C. for 15 h.

[0036] a) Preparation of Mg—Al hydrotalcite (LDH) tungstate (CatalystA):

[0037] To reach anion exchange of degree of 12%, 1 g of Mg—Al—Clhydrotalcite was stirred in 100 ml of aqueous solution of 1.87 mM (0.616g) sodium tungstate (obtained from M/s. Fluka, a Sigma Aldrich Company,Switzerland), at 293 K for 24 h. The solid catalyst was filtered, washedwith deionised and decarbonated water and lyophilized to dryness.

[0038] b) Preparation of Mg—Al hydrotalcite (LDH) molybdate (CatalystB):

[0039] To reach anion exchange of degree of 12%, 1 g of Mg—Al—Clhydrotalcite was stirred in 100 ml of aqueous solution of 1.87 mM (0.452g) sodium molybdate (obtained from M/s. Fluka, a Sigma Aldrich Company,Switzerland), at 293 K for 24 h. The solid catalyst was filtered, washedwith deionised and decarbonated water and lyophilized to dryness.

[0040] c) Preparation of Mg—Al hydrotalcite (LDH) vanadate (Catalyst C):

[0041] To reach anion exchange of degree of 12%, 1 g of Mg—Al—Clhydrotalcite is stirred in 100 ml of aqueous solution of 1.87 mM (0.456g) sodium vanadate (obtained from M/s. Fluka, a Sigma Aldrich Company,Switzerland), at 293 K for 24 h. The solid catalyst was filtered, washedwith deionised and decarbonated water and lyophilized to dryness.

2. Preparation of Mg—Al hydrotalcite (LDH) nitrate

[0042] Magnesium nitrate hexahydrate (30.8 g, 0.12 mol) and aluminiumnitrate nonahydrate (15.0 g, 0.04 mol) were dissolved in 100 ml ofdeionised and decarbonated water. The pH of the solution was adjusted to10 by adding 2M NaOH. The resulting suspension was stirred for 2 h atroom temperature. The precipitate hydrotalcite was collected byfiltration under N₂ atmosphere and dried overnight at 80° C.

[0043] a) Preparation of Mg—Al hydrotalcite (LDH) tungstate (CatalystD):

[0044] To reach anion exchange of degree of 12%, 1 g of Mg—Al—NO₃hydrotalcite was stirred in 100 ml of aqueous 1.87 mM (0.616 g) sodiumtungustate (obtained from M/s. Fluka, a Sigma Aldrich Company,Switzerland), at 293 K for 24 h. The solid catalyst was filtered, washedwith of deionised and decarbonated water and lyophilized to dryness.

3. Preparation of Mg—Al hydrotalcite (LDH) carbonate

[0045] Mg—Al—CO₃ hydrotalcite (3:1) is prepared as follows: An aqueoussolution (0.280 l) containing Mg(NO₃)₂.6H₂O (0.2808 mol) andAl(NO₃)₃.9H₂O (0.093 mol) (obtained from M/s. Fluka, a Sigma AldrichCompany, Switzerland) was added slowly to a second solution (0.280 l)containing NaOH (0.6562 mol) and Na₂CO₃ (0.3368 mol) in a 1.0 l roundbottomed flask under vigorous stirring. The addition took nearly 3 h.Then the slurry was heated to 338 K for 16 h. The precipitate formed wasfiltered off and washed with hot distilled water until the pH of thefiltrate was 7. The precipitate was dried in an oven at 353 K for 15 h.

[0046] a) Preparation of Mg—Al hydrotalcite (LDH) tungstate (CatalystE):

[0047] To reach anion exchange of degree of 12%, 1 g of Mg—Al—CO₃calcined (at 723 K for 6 h in a flow of air) hydrotalcite was stirred in100 ml of aqueous solution of 1.87 mM (0.616 g) sodium tungstate(obtained from M/s. Fluka, a Sigma Aldrich Company, Switzerland), at 293K for 24 h. The solid catalyst was filtered, washed with deionised anddecarbonated water and lyophilized to dryness.

4. Preparation of Ni—Al hydrotalcite (LDH) chloride

[0048] Ni—Al hydrotalcite chloride (3:1) was prepared as follows: About200 ml of decarbonated and deionised water was taken into a 1 liter fournecked round bottomed flask and stirred at 25° C. with a magneticstirrer under nitrogen flow. A mixture (Al³⁺=0.05 mol/l), (Ni²⁺=0.15mol/l) of decarbonated solution of AlCl₃.9H₂O (12.07 g), NiCl₂.6H₂O(35.65 g) (obtained from M/s. Fluka, a Sigma Aldrich Company,Switzerland) and aqueous solution of sodium hydroxide (16 g 0.2 mol/l)were added continuously drop-wise from a burette, the pH of the reactionmixture being kept at 10.00-10.2 during the reaction. The precipitateobtained was filtered, washed with deionised and decarbonated water anddried at 70° C. for 15 h.

[0049] a) Preparation of Ni—Al hydrotalcite (LDH) tungstate (CatalystF):

[0050] To reach anion exchange of degree of 12%, 1 g of Ni—Alhydrotalcite chloride was stirred in 100 ml of aqueous 1.87 mM (0.616 g)sodium tungstate (obtained from M/s. Fluka, a Sigma Aldrich Company,Switzerland), at room temperature for 24 h. The solid catalyst wasfiltered, washed with deionised and decarbonated water and lyophilizedto dryness.

5. Preparation of Ni—Al hydrotalcite (LDH) nitrate

[0051] Nickel nitrate hexahydrate (34.8 g, 0.12 mol) and aluminiumnitrate nonahydrate (15.0 g, 0.04 mol) were dissolved in 100 ml ofdeionised and decarbonated water. The pH of the solution was adjusted to10 by adding 2M NaOH. The resulting suspension was stirred for 2 h atroom temperature. The precipitate hydrotalcite was collected byfiltration under N₂ atmosphere and dried overnight at 80° C.

[0052] a) Preparation of Ni—Al hydrotalcite (LDH) tungstate (CatalystG):

[0053] To reach anion exchange of degree of 12%, 1 g of Ni—Al—NO₃hydrotalcite was stirred in 100 ml of aqueous 1.87 mM (0.616 g) sodiumtungustate (obtained from M/s. Fluka, a Sigma Aldrich Company,Switzerland), at 293 K for 24 h. The solid catalyst was filtered, washedwith of deionised and decarbonated water and lyophilized to dryness.

6. Preparation of Bu₄N)₃PO₄[WO(O₂)₂]₄

[0054] Hydrogen peroxide (30% w/w) 100 mmol (10 ml) was added to asolution of H₃[PW₁₂O₄₀]6 mmol of tungsten (or 1.65 g) in 1 ml of water.After 30 min an aqueous solution of tetrabutylammonium chloride (1.6mmol) was slowly added. The resulting white precipitate was filtered outand washed with several times with water then air-dried.

[0055] a) Preparation of LDH-{[PO₄WO(O₂)]₄}(Catalyst H):

[0056] The above synthesized complex (0.46 mmol) was exchanged on 1.0 gof Mg—Al—Cl LDH in 3 ml of water, to this 1 ml of hydrogen peroxide(30%, w/w) was added drop-wise and stirring was continued for 16 h atroom temperature. Finally the catalyst was filtered and washed withwater and water-acetone (1:1), acetone and dried on vacuum.

EXAMPLE 2 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0057] The four-necked flask was charged with 0.22 ml (2 mmol) ofN-methylmorpholine, 200 mg of catalyst A and 50 ml of water. To themixture was added dropwise 6.6 ml (6 mmol) of a 30% by weight of aqueoussolution of hydrogen peroxide for period of 0.5 hours in 2 to 3 portionsat 25° C. under continuous stirring. Continued the reaction for another0.5 hour. After the completion of the reaction (followed by TLC), thecatalyst was filtered off and washed with methanol. To the filtrate asmall amount of manganese dioxide was added to decompose the unreactedhydrogen peroxide. The treated reaction mixture was filtered to removethe solid MnO₂ and concentrated under reduced pressure to obtain theproduct. The product thus obtained was purified by column chromatographyto afford the corresponding amine oxide. N-methylmorpholine N-oxide of96% yield was obtained. This product is commercially available fromFluka, Aldrich, Lancaster and Merck companies.

EXAMPLE 3 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide: recycle-I

[0058] The oxidation reaction of N-methylmorpholine by using catalyst Awhich had been used in example 2 was performed in an identical procedureas detailed in example 2, without further addition of fresh catalyst.N-methylmorpholine N-oxide of 96% yield was obtained.

EXAMPLE 4 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide: recycle-II

[0059] The oxidation reaction of N-methylmorpholine by using catalyst Awhich had been used in example 3 was performed in an identical procedureas detailed in example 2, without further addition of fresh catalyst.N-methylmorpholine N-oxide of 95% yield was obtained.

EXAMPLE 5 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide: recycle-III

[0060] The oxidation reaction of N-methylmorpholine by using catalyst Awhich had been used in example 4 was performed in an identical procedureas detailed in example 2, without further addition of fresh catalyst.N-methylmorpholine N-oxide of 94% yield was obtained.

EXAMPLE 6 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide: recycle-IV

[0061] The oxidation reaction of N-methylmorpholine by using catalyst Awhich had been used in example 5 was performed in an identical procedureas detailed in example 2, without further addition of fresh catalyst.N-methylmorpholine N-oxide of 94% yield was obtained.

EXAMPLE 7

[0062] Oxidation of N-methylmorpholine catalysed by tungstate exchangedwith Mg/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide: recycle-V

[0063] The oxidation reaction of N-methylmorpholine by using catalyst Awhich had been used in reaction 6 in an identical procedure as detailedin example 2, without further addition of fresh catalyst.N-methylmorpholine N-oxide of 95% yield was obtained.

EXAMPLE 8 Oxidation of N-methylmorpholine catalysed by molybdateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0064] The oxidation reaction of N-methylmorpholine was performed usingcatalyst B in an identical procedure as detailed in Example 2. The timetaken for the completion of reaction was 3.5 hours. N-methylmorpholineN-oxide of 90% yield was obtained.

EXAMPLE 9 Oxidation of N-methylmorpholine catalysed by vanadateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0065] The oxidation reaction of N-methylmorpholine was performed usingcatalyst C in an identical procedure as detailed in Example 2. The timetaken for the completion of reaction was 3.5 hours. N-methylmorpholineN-oxide of 40% yield was obtained.

EXAMPLE 10 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0066] The oxidation reaction of N-methylmorpholine was performed usingcatalyst D in an identical procedure as detailed in Example 2.N-methylmorpholine N-oxide of 95% yield was obtained.

EXAMPLE 11 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0067] The oxidation reaction of N-methylmorpholine was performed usingcatalyst E in an identical procedure as detailed in Example 2.N-methylmorpholine N-oxide of 96% yield was obtained.

EXAMPLE 12 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0068] The oxidation reaction of N-mtehylmorpholine was performed usingcatalyst F in an identical procedure as detailed in Example 2. The timetaken for the completion of reaction was 1.5 hours. N-methylmorpholineN-oxide of 95% yield was obtained.

EXAMPLE 13 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0069] The oxidation reaction of N-methylmorpholine was performed usingcatalyst G in an identical procedure as detailed in Example 2. The timetaken for the completion of reaction was 1.5 hours. N-methylmorpholineN-oxide of 95% yield was obtained.

EXAMPLE 14 Oxidation of N-methylmorpholine catalysed byLDH-{[PO₄WO(O₂)]₄}

[0070] The oxidation reaction of N-methylmorpholine was performed usingcatalyst H in an identical procedure as detailed in Example 2. The timetaken for the completion of reaction was 3.5 hours. N-methylmorpholineN-oxide of 40% yield was obtained.

EXAMPLE 15 Oxidation of N-methylmorpholine catalysed by Na₂WO₄

[0071] The oxidation reaction of N-methylmorpholine was performed usingNa₂WO₄ in an identical procedure as detailed in Example 2. The timetaken for the completion of reaction was 3.5 hours. N-methylmorpholineN-oxide of 75% yield was obtained.

EXAMPLE 16 Oxidation of N-methylmorpholine catalysed by Na₂VO₃

[0072] The oxidation reaction of N-methylmorpholine was performed usingNa₂VO₃ in an identical procedure as detailed in Example 2. The timetaken for the completion of reaction was 3.5 hours. N-methylmorpholineN-oxide of 15% yield was obtained.

EXAMPLE 17 Oxidation of N-methylmorpholine catalysed by Na₂MoO₄

[0073] The oxidation reaction of N-methylmorpholine was performed usingNa₂MoO₄ in an identical procedure as detailed in Example 2. The timetaken for the completion of reaction was 3.5 hours. N-methylmorpholineN-oxide of 48% yield was obtained.

EXAMPLE 18 Oxidation of N-methylmorpholine catalysed by tungstateexchanged with Mg/Al(3:1) layered double hydroxides using aqueoushydrogen peroxide

[0074] The four-necked flask was charged with 0.22 ml (2 mmol) ofN-methylmorpholine, 200 mg of catalyst A and 50 ml of water. To this 6mg of dodecylbenzenesulfonic acid sodium salt was added as surfactantwas added as surfactant. To the mixture was added dropwise 6.6 ml (6mmol) of a 30% by weight of aqueous solution of hydrogen peroxide forperiod of 0.5 hours in 2 to 3 portions at 25° C. under continuousstirring. Continued the reaction for another 0.5 hour. After thecompletion of the reaction (followed by TLC), the catalyst was filteredoff and washed with methanol. To the filtrate a small amount ofmanganese dioxide was added to decompose the unreacted hydrogenperoxide. The treated reaction mixture was filtered to remove the solidMnO₂ and concentrated under reduced pressure to obtain the product. Theproduct thus obtained was purified by column chromatography to affordthe corresponding amine oxide. N-methylmorpholine N-oxide of 96% yieldwas obtained. This product is commercially available from Fluka,Aldrich, Lancaster and Merck companies.

EXAMPLE 19 Oxidation of triethyl amine catalysed by tungstate exchangedwith Mg/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide

[0075] The oxidation reaction of triethyl amine by using catalyst A wasperformed in an identical procedure as detailed in example 2. The timetaken for the completion of reaction was 3 hours. Triethyl amine N-oxideof 96% yield was obtained.

EXAMPLE 20 Oxidation of triethyl amine catalysed by tungstate exchangedwith Mg/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide

[0076] The oxidation reaction of triethyl amine by using catalyst A wasperformed in an identical procedure as detailed in example 18. The timetaken for the completion of reaction was 1.5 hours. Triethyl amineN-oxide of 96% yield was obtained.

EXAMPLE 21 Oxidation of tributyl amine catalysed by tungstate exchangedwith Mg/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide

[0077] The oxidation reaction of tributyl amine was performed by usingcatalyst A in an identical procedure as detailed in example 2. The timetaken for the completion of reaction was 3 hours. Tributyl amine N-oxideof 94% yield was obtained.

EXAMPLE 22 Oxidation of N,N-dibutyl benzylamine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0078] The oxidation reaction of N,N-dibutyl benzylamine was performedby using catalyst A in an identical procedure as detailed in example 2.The time taken for the completion of reaction was 1.5 hours. N,N-dibutylbenzyl amine N-oxide of 96% yield was obtained.

EXAMPLE 23 Oxidation of N,N-dibutyl benzylamine catalysed by tungstateexchanged with Mg Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0079] The oxidation reaction of N,N-dibutyl benzylamine was performedby using catalyst A in an identical procedure as detailed in example 18.N,N-dibutyl benzyl amine N-oxide of 95% yield was obtained.

EXAMPLE 24 Oxidation of N-benzyl piperidine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0080] The oxidation reaction of N-benzyl piperidine was performed byusing catalyst A, in an identical procedure as detailed in example 2.The time taken for the completion of reaction was 3 hours. N-benzylpiperidine N-oxide of 97% yield was obtained.

EXAMPLE 25 Oxidation of N-benzyl piperidine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0081] The oxidation reaction of N-benzyl piperidine was performed byusing catalyst A, in an identical procedure as detailed in example 18.N-benzyl piperidine N-oxide of 97% yield was obtained.

EXAMPLE 26 Oxidation of N,N-dimethyldecylamine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0082] The oxidation reaction of N,N-dimethyldecylamine was performed byusing catalyst A in an identical procedure as detailed in example 2. Thetime taken for the completion of reaction was 2.5 hours.N,N-dimethyldecylamine N-oxide of 97% yield was obtained. This productis commercially available from Lonza Inc., With trade name Barlox 10S(Specification: 30 weight percent decyldimethyl tertiary amine oxide).

EXAMPLE 27 Oxidation of N,N-dimethyloctylamine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0083] The oxidation reaction of N,N-dimethyloctylamine was performed byusing catalyst A in an identical procedure as detailed in example 2. Thetime taken for the completion of reaction was 2.5 hours.N,N-dimethyloctylamine N-oxide of 95% yield was obtained.

EXAMPLE 28 Oxidation of N,N-dimethyloctylamine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0084] The oxidation reaction of N,N-dimethyloctylamine was performed byusing catalyst A in an identical procedure as detailed in example 18.N,N-dimethyloctylamine N-oxide of 95% yield was obtained.

EXAMPLE 29 Oxidation of N,N-dimethyl benzylamine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0085] The oxidation reaction of N,N-dimethyl benzylamine was performedby using catalyst A in an identical procedure as in Example 2. The timetaken for the completion of reaction was 1.5 hours. N,N-dimethylbenzylamine amine N-oxide of 95% yield was obtained

EXAMPLE 30 Oxidation of N,N-dimethyl benzylamine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0086] The oxidation reaction of N,N-dimethyl benzylamine was performedby using catalyst A in an identical procedure as in example 18.N,N-dimethyl benzylamine amine N-oxide of 96% yield was obtained

EXAMPLE 31 Oxidation of N,N-dimethylcyclohexylamine catalysed bytungstate exchanged with Mg/Al (3:1) layered double hydroxides usingaqueous hydrogen peroxide

[0087] The oxidation reaction of N,N-dimethylcyclohexylamine by usingcatalyst A was performed in an identical procedure as detailed inexample 2. The time taken for the completion of reaction was 3 hours.N,N-dimethylcyclohexylamine N-oxide of 96% yield was obtained.

EXAMPLE 32 Oxidation of N,N-dimethylcyclohexylamine catalysed bytungstate exchanged with Mg/Al (3:1) layered double hydroxides usingaqueous hydrogen peroxide

[0088] The oxidation reaction of N,N-dimethylcyclohexylamine by usingcatalyst A was performed in an identical procedure as detailed inexample 18. N,N-dimethylcyclohexylamine N-oxide of 95% yield wasobtained.

EXAMPLE 33 Oxidation of dibutyl amine catalysed by tungstate exchangedwith Mg/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide

[0089] The oxidation reaction of dibutyl amine was performed by usingcatalyst D in an identical procedure as detailed in example 2. The timetaken for the completion of reaction was 3 hours.N-butylidene-butylamine N-oxide of 96% yield was obtained.

EXAMPLE 34 Oxidation of dibutyl amine catalysed by tungstate exchangedwith Mg/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide

[0090] The oxidation reaction of dibutyl amine was performed by usingcatalyst E in an identical procedure as detailed in example 2. The timetaken for the completion of reaction was 3 hours.N-butylidene-butylamine N-oxide of 95% yield was obtained.

EXAMPLE 35 Oxidation of dibutyl amine catalysed by tungstate exchangedwith Ni/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide

[0091] The oxidation reaction of dibutyl amine was performed by usingcatalyst F in an identical procedure as detailed in example 2. The timetaken for the completion of reaction was 3 hours.N-butylidene-butylamine N-oxide of 96% yield was obtained.

EXAMPLE 36 Oxidation of dibutyl amine catalysed by tungstate exchangedwith Ni/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide

[0092] The oxidation reaction of dibutyl amine was performed by usingcatalyst G in an identical procedure as detailed in example 2. The timetaken for the completion of reaction was 3 hours.N-butylidene-butylamine N-oxide of 95% yield was obtained.

EXAMPLE 37 Oxidation of dibutyl amine catalysed by tungstate exchangedwith Mg/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide

[0093] The oxidation reaction of dibutyl amine was performed by usingcatalyst A in an identical procedure as detailed in example 2. The timetaken for the completion of reaction was 3 hours.N-butylidene-butylamine N-oxide of 97% yield was obtained.

EXAMPLE 38 Oxidation of dibenzyl amine catalysed by tungstate exchangedwith Mg/Al (3:1) layered double hydroxides using aqueous hydrogenperoxide

[0094] The oxidation reaction of dibenzyl amine was performed by usingof catalyst A in an identical procedure as detailed in example 2. Thetime taken for the completion of reaction was 5 hours.N-benzylidenebenzylamine N-oxide of 60% yield was obtained.

EXAMPLE 39 Oxidation N-benzyl phenethylamine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0095] The oxidation reaction of N-benzyl phenethylamine was performedby using catalyst A in an identical procedure as in example 2. The timetaken for the completion of reaction was 6 hours. N-(1-methylbenzylidine) phenylamine N-oxide of 90% yield was obtained.

EXAMPLE 40 Oxidation of N-phenyl benzylamine amine catalysed bytungstate exchanged with Mg/Al (3:1) layered double hydroxides usingaqueous hydrogen peroxide

[0096] The reaction oxidation reaction of N-phenyl benzylamine wasperformed by using catalyst A in an identical procedure as detailed inexample 2. The time taken for the completion of reaction was 4 hours.N-bezylidine phenylamine N-oxide of 93% yield was obtained.

EXAMPLE 41 Oxidation piperidine catalysed by tungstate exchanged withMg/Al (3:1) layered double hydroxides using aqueous hydrogen peroxide

[0097] The oxidation reaction of piperidine by using catalyst A wasperformed in an identical procedure as detailed in example 2. The timetaken for completion of reaction was 3 hours. 2,3,4,5 tetrahydropyridine N-oxide of 92% yield was obtained.

EXAMPLE 42 Oxidation of 1,2,3,4-tetrahydroisoquinoline catalysed bytungstate exchanged with Mg/Al (3:1) layered double hydroxides usingaqueous hydrogen peroxide

[0098] The oxidation reaction of 1,2,3,4-tetrahydroisoquinolineperformed by using catalyst A in an identical procedure as detailed inexample 2. The time taken for completion of reaction was 5 hours. 3,4dihydroisoquinoline N-oxide of 93% yield was obtained.

EXAMPLE 43 Oxidation of diisopropyl amine catalysed by tungstateexchanged with Mg/Al (3:1) layered double hydroxides using aqueoushydrogen peroxide

[0099] The reaction oxidation reaction of diisopropyl amine wasperformed by using catalyst A in an identical procedure as detailed inexample 2. The time taken for the completion of reaction was 3 hours.N-(1-methylethylidine)-1-methylethylamine N-oxide of 92% yield wasobtained. TABLE 1 Reusability of the catalyst in the oxidation ofN-methylmorpholine catalysed by tungstate exchanged with Mg/Al (3:1)layered double hydroxides (Catalyst A) using aqueous hydrogenperoxide^(a) Ex. No Tertiary amine Cycle Time(h) Amine oxide Yield^(b) 2N- 1 1.0 N-methylmorpholine 96 methylmorpholine N-oxide 3 N- 2 1.0N-methylmorpholine 95 methylmorpholine N-oxide 4 N- 3 1.0N-methylmorpholine 94 methylmorpholine N-oxide 5 N- 4 1.0N-methylmorpholine 94 methylmorpholine N-oxide 6 N- 5 1.0N-methylmorpholine 94 methylmorpholine N-oxide 7 N- 6 1.0N-methylmorpholine 95 methylmorpholine N-oxide

[0100] TABLE 2 The catalytic N-oxidation of N-methylmorpholine toN-methylmorpholine N-oxide in water using various metal ion-exchangedLDH catalysts and their homogeneous analogues^(a) Ex. No Catalyst Time(h) Yield^(b)  8 LDH-MoO₄ ²⁻ (Catalyst B) 3.5 90  9 LDH-VO₃ ⁻ (CatalystC) 3.5 40 10 LDH-WO₄ ²⁻ (Catalyst D) 1.0 95 11 LDH-WO₄ ²⁻ (Catalyst E)1.0 96 12 Ni-Al-LDH-WO₄ ²⁻ (Catalyst F) 1.5 95 13 Ni-Al-LDH-WO₄ ²⁻(Catalyst G) 1.5 96 14 LDH-{PO₄WO(O₂)]₄} (Catalyst H) 3.5 40 15 Na₂WO₄3.5 75 16 NaVO₃ 3.5 15 17 Na₂MoO₄ 3.5 48

[0101] TABLE 3 N-oxidation of aliphatic tert-amines catalysed by LDH-WO₄²⁻ (Catalyst A) in water^(a) (procedure I) or water in combination ofdodecylbenzenesufonicacid sodium salt^(b) (procedure II). Ex. NoTertiary amine Procedure Amine oxide Time(h) Yield^(c) 18 N-methyl IIN-methylmorpholine N- 1.0 96 morpholine oxide 19 Triethyl amine ITriethyl amine N-oxide 3.0 96 20 Triethyl amine II Triethyl amineN-oxide 1.5 96 21 Tributyl amine I Tributyl amine N-oxide 3.0 94 22N,N-dibutyl I N,N-dibutyl benzyl amine 1.5 96 benzyl amine N-oxide 23N,N-dibutyl II N,N-dibutyl benzyl amine 1.0 95 benzyl amine N-oxide 24N-benzyl I N-benzyl piperidine N- 3.0 97 25 piperidine II oxide 1.0 97N-benzyl N-benzyl piperidine N- piperidine oxide 26 N,N-dimethyl IN,N-dimethyl decyl amine 2.5 97 decyl amine N-oxide 27 N,N-dimethyl IN,N-dimethyl octyl amine 2.5 95 octyl amine N-oxide 28 N,N-dimethyl IIN,N-dimethyl octyl amine 1.0 95 octyl amine N-oxide 29 N,N-dimethyl IN,N-dimethyl benzyl 1.5 95 benzyl amine amine 30 N,N-dimethyl II N-oxide1.0 96 benzyl amine N,N-dimethyl benzyl amine N-oxide 31 N,N-dimethyl IN,N-dimethyl 3.0 96 cyclohexylamine yclohexylamine 32 N,N-dimethyl IIN-oxide 1.0 95 cyclohexylamine N,N-dimethyl yclohexylamine N-oxide

[0102] TABLE 4 Oxidation of secondary amines catalysed by anion oftransition metal oxides exchanged layered double hydroxides usingaqueous hydrogen peroxide^(a) Ex.No Secondary amine Catalyst Amine oxide(nitrone) Time(h) Yield^(b) 33 Dibutyl amine D N-butylidene-butylamine 396 N-oxide 34 Dibutyl amine E N-butylidene-butylamine 3 95 N-oxide 35Dibutyl amine F N-butylidene-butylamine 3 96 N-oxide 36 Dibutyl amine GN-butylidene-butylamine 3 95 N-oxide 37 Dibutyl amine AN-butylidene-butylamine 3 97 N-oxide 38 Dibenzyl amine AN-butylidene-butylamine 5 60 benzylamine N-oxide 39 N-benzyl AN-(1-methylbenzylidene) 6 90 phenethyl amine benzylamine N-oxide 40N-Phenyl benzyl A N-benzylidene 4 93 amine phenylamine N-oxide 41Piperidine A 2,3,4,5 Tetrahydro 3 92 pyridine N-oxide 42 1,2,3,4Tetrahydro A 3,4, Dihydroisoquinoline 5 93 isoquinoline N-oxide 43Diisopropyl amine A N-1-ethylethylidene) 1- 3 92 methylethylamineN-oxide

[0103] The main advantages of the present invention are:

[0104] 1. The present process is eco-friendly and simple.

[0105] 2. The catalyst is cheap, non-corrosive, recyclable for severaltimes and heterogeneous in nature.

[0106] 3. The reactions are conducted in water, an eco-friendly benignsolvent.

[0107] 4. The reaction conditions are very mild, being the reactiontemperature ranges between 10-25° C.

[0108] 5. The hydrogen peroxide used is 30% by weight, which is moreenvironmentally friendly.

[0109] 6. The process is economical and is accomplished in short timewith high productivity.

[0110] 7. The amount of effluents formed in this process is minimizedbecause the catalyst and solvent are recovered/recycled and reused.

[0111] 8. The process provides high quality of the product withoutresulting in gel formation, during the course of reaction.

We claim:
 1. A process for the preparation of high quality amine oxidewhich comprises reacting a tertiary or secondary amine with hydrogenperoxide as an oxidant in presence of a recyclable heterogeneous layereddouble hydroxide exchanged with one of the anions of transition metaloxides as a catalyst in a solvent selected from the group consisting ofwater, water containing dodecylbenzenesulfonic acid sodium salt asadditive, and a water miscible organic solvent at a temperature rangingbetween 10-25° C. for a period of 1-6 hours under continuous stirringand separating the product by simple filtration and subsequentlyevaporation of solvents.
 2. A process as claimed in claim 1 wherein theheterogeneous catalyst used is layered double hydroxide with transitionmetal oxides selected from a group consisting of tungstate, molybdate,vanadate and their polyanions as polyoxometalates having formula I:[M^(II) _((1-x))M^(III) _(x)(OH)₂][M^(n−)]_(x/2).zH₂O, which is derivedfrom LDH having formula II [M^(II) _((1-x))M^(III)_(x)(OH)₂][A^(n−)]_(x/2).zH₂O where M is an anion of transition metaloxide selected from a group consisting of W, Mo, V and A^(n−) is aninterstitial anion, selected from nitrate, chloride and M^(II) is adivalent cation selected from the group consisting of Mg²⁺, Mn²⁺, Fe²⁺,V²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ Pd²⁻, or Ca²⁺ and M^(III) is a trivalent ionselected from the group consisting of Al³⁺, Cr³⁺, V³⁺, Mn³⁺, Fe³⁺, Co³⁺,Ni³⁺, Rh³⁺, Ru³⁺, Ga³⁺ or La³⁺, x is the mole fraction having integralvalue ranging from 0.2 to 0.33 and z is the number of water moleculesand ranges from 1 to
 4. 3. A process as claimed in claim 1 wherein thetertiary amines, having the general formula R¹R²NR³ wherein R¹, R² andR³ are the same or different and are straight-chain or branched-chaingroups selected from alkyl, alkenyl and aralkyls having C₁-C₂₄ carbonsselected from dimethyl decyl amine, dimethyl docyl amine,dimethylbenzylamine, cyclic amines from imidazolines pyrididines,N-substituted piperazinesm, or N-substituted morpholines such asN-methylmorpholine.
 4. A process as claimed in claim 1 where in thesecondary amines used in the system have the general formula R¹R²NHwherein R¹ and R² may be the same or different and are thestraight-chain or branched chain groups selected from alkyl, alkenyl andaralkyls having C₁-C₂₄ carbons selected from dibutyl amine, dibenzylamine, N-benzyl phenethylamine, N-phenyl benzylamine, cyclic aminesselected from piperidine, 1,2,3,4 tetrahydro isoquinoline.
 5. A processas claimed in claim 1 wherein 30% by weight of aqueous hydrogen peroxideis added slowly in a controlled manner during the period specified.
 6. Aprocess as claimed in claim 1 wherein the catalyst introduced in thesystem is 6-12 weight % anion of transition metal oxides selected fromtungstate, molybdate, vanadate and their polyanions as polyoxometalates.7. A process as claimed in claim 1 wherein the water miscible organicsolvents used for the reaction are selected from the group consisting ofmethanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol andisobutyl alcohol.
 8. A process as claimed in claim 1 wherein the amountof hydrogen peroxide used ranges between 2 to 6 moles per mole ofsecondary or tertiary amine.